This invention relates to printed wiring boards to be built in or fitted to IC cards used as bank cards, identification cards, medical examination cards or the like. More particularly, this invention relates to a printed wiring board for IC cards having so-called IC chips processing and storing various information from a read-writer for IC cards and external contact terminals for transmitting and receiving by electric signals the above mentioned various informations for these IC chips.
Generally, the devices for transmitting and receiving information with the above mentioned read-writer for IC cards are largely divided into two types, a contact type transmitting and receiving electric signals through wires and a non-contact type using such wireless signals as electromagnetic wave, magnetic or optical signals on the way. The present invention relates particularly to the former.
The printed wiring board for IC cards of this type to be built in or fitted to an IC card has external contact terminals required to transmit and receive information from a read-writer for the IC card for the IC chips mounted on the board and a conductor circuit electrically connecting the external contact terminals with the IC chips or the like.
Before explaining the printed wiring board for IC cards according to the present invention, there shall be explained an IC module wherein IC chips or the like are mounted on a printed wiring board for IC cards and an IC card itself in which the IC module is built or fitted. For reliability and user convenience this kind of IC card is required to meet the following respective requirements:
(1) The IC card of this kind must be properly small and thin as a whole so as to be easily carried, controlled and inserted into the above read-writer for IC cards.
For this requirement, presently all IC cards are made about 0.76 mm thick so as to conform to the size of commonly used bank cards and the like. As the thickness of the IC chips arranged within the IC card is more than 0.25 mm at present, the thickness of the IC module except the external contact terminal is now more than 0.3 mm.
(2) The IC card of this kind must be electrically and frequently contacted with the read-writer for IC cards by the external contact terminals exposed on the surface and therefore the external contact terminals must be always high in the durability and electric contact in the operation.
(3) The IC card of this kind must be small and thin as explained in (1) above. In such case, the IC card will be likely to be curved during the use. Even in case the IC card is thus curved, the conductor circuit for the IC chips built in or fitted to the IC card must not be broken and the IC module provided with the IC chips must not be removed from the IC card.
(4) In the IC card of this kind, as described in (2) above, the external contact terminals are exposed but contact with water and dust which would adversely influence the IC chips must not easily enter the IC card.
The IC card of this kind is basically formed of a sheet-shaped card material which is a base material formed of such plastics as vinyl chloride and an IC module including IC chips and a printed wiring board. Particularly, in the case of a contact type IC card, the external contact terminals for transmitting and receiving electric signals must be exposed on the surface of the IC card as described above. The method of joining the sheet-shaped card material with the IC module to produce IC cards has progressed step by step and this historical development can be largely divided into three kinds as shown in the study "Trend of Development of the Multifunctional Card System and New Application Field" made by Japan Industrial Technical Center on Mar. 13 and 14, 1984 and in FIGS. 18 to 20 based on the same.
FIGS. 18 to 20 show vertically sectioned views of the structures of IC cards joined by respective joining methods. The development steps of IC cards are shown in the order of these views.
FIG. 18 shows a partly magnified vertically sectioned view of an IC card wherein a predetermined through hole is formed in a sheet-shaped card material 31 and an IC module 12 is joined within this through hole and shows that the IC module 12 and the sheet-shaped card material 31 are joined with each other only on the side wall. Therefore, the IC card shown in FIG. 18 is likely to be simply removed from the sheet-shaped card material 31 and can satisfy the requirement of (1) above but can not satisfy the requirement of (3) above. The thickness of the IC card is less than 1 mm, accordingly, it does not hold together well and the practical range of use is narrow.
FIG. 19 shows a partly magnified vertically sectioned view of an IC card disclosed, for example, in the Unexamined Japanese Patent Publication laid open No. 210494/1982. In the IC card shown in this drawing, a recess is formed in the sheet-shaped card material 31 and an IC module 12 is fitted in this recess and is laminated on the underside with an over sheet 32. This IC module 12 is fitted in the recess of the sheet-shaped card material 31 so that the upper surface together with the external contact terminal (to which the conductor circuit 13 itself on the IC module 12 corresponds) formed on it may be exposed on the surface of the card. That is to say, it is disclosed in the above mentioned Unexamined Japanese Patent Publication laid open No. 210494/1982 that the IC module 12 is inserted and bonded in a recess formed in the sheet-shaped card material 31 by using a blade. However, the IC card of this type has a defect that, in case the card is bent so as to be convex upward, the IC module 12 will spring out and can not satisfy the requirement of (3) above.
FIG. 20 shows a partly magnified vertically sectioned view of an IC card disclosed, for example, in the Unexamined Japanese Patent Publication laid open No. 26541/1981. The IC card shown in this drawing shall be temporarily called a "laminated type". In this laminated type IC card, over sheets 32 are bonded on both upper and lower surfaces of the IC module 12 and an aperture is formed in the upper side over sheet 32 to expose the conductor circuit 13 to be an external contact terminal part. It is disclosed in the above mentioned Unexamined Japanese Patent publication laid open No. 26541/1981 that, in the IC card shown in FIG. 20, the over sheet 32 in which only the part corresponding to the external contact terminal is cut off is bonded on the IC module 12. The IC card shown in the Unexamined Japanese Patent Publication laid open No. 26541/1981 can satisfy the requirement of (3) above to some extent but is not satisfactory for the following reasons.
In order to prevent the IC module 12 from springing out the IC card is bent, in case the thickness of the over sheet must be at least 0.1 mm and, if possible, more than 0.15 mm when the oversheet 32 is made of the typically used vinyl chloride. This conclusion is supported by the bending standard test in the interim report of "ISO/TC 97/SC 17 Identification and Credit Cards" June, 1984. As the thickness of the over sheet 32 used for this IC card must be more than 0.1 mm, the thickness of the external contact terminal of the IC module 12 coated with this over sheet 32 must be at least 0.1 mm. Unless the external contact terminal is of such thickness, the external contact terminal part will be positioned below the surface of the IC card by the thickness of the over sheet 32, therefore the problem of dust accumulating in the recess formed thereby will occur as the IC card is used and the electric contact reliability of the external contact terminal will become very low.
As described above, in order to satisfy the requirements of (1) to (4) above in the IC card, the amount of the projection from the IC module 12 surface of the external contact terminal formed on the IC module 12 must be more than is predetermined (at least 0.1 mm). In other words, in the printed wiring board for IC cards according to the present invention, the amount of the projection of the external contact terminal is required to be at least 0.1 mm.
Also, as described above, the total thickness allowable in this kind of IC card is 0.76 mm. As the thickness of the IC chip is usually more than 0.25 mm, the thickness of the IC module 12 less the external contact terminal is required to be more than 0.3 mm. Therefore, in the IC card of the type laminated with the over sheets 32 on both surfaces, the thickness of the over sheets 32 on the front and back is less than 0.46 mm. Furthermore, the over sheets 32 on the front and back may be substantially of the same thickness in order to prevent warping. Therefore, the thickness of the over sheet 32 on the external contact terminal side is less than 0.23 mm. The thickness of the external contact terminal corresponding to it may be likewise less than 0.23 mm. However, in case this external contact terminal and the conductor curcuit 13 are simultaneously formed, in consideration of the fact that the thickness of the conductor circuit 13 which must be laminated with the over sheet 32 so as not to protrude is 0.025 to 0.07 mm, the thickness of the external contact terminal must be about 0.3 mm.
The question of increasing the thickness of the external contact terminal in IC cards of this type is not addressed in the above mentioned respective data and in the data related to the field.
The Unexamined Japanese Patent Publication laid open No. 26451/1981 (filed on May 17, 1979 by claiming priority based on West German Application No. P2920012.2 and laid open in Japan on Mar. 14, 1981), discloses an identification card wherein IC chips for processing electric signals are provided and are fitted to separate supporting members inserted in a window, characterized in that the thickness of said supporting member is made substantially equal to that of the identification card, said IC chips are arranged within said supporting members, the shape of said window is made similar to the shape of said supporting member, said window is made larger than said supporting member so that said supporting member may be enclosed with a gap and said supporting member is supported within said window by a basically elastic coupling member.
Particularly in FIG. 2 of this technical data is mentioned "contact surface 20" thought to correspond to the external contact terminal at issue in the present invention. However, the necessity for and formation of this "contact surface 20" are never thoroughly addressed.
Further, in the Unexamined Japanese Patent Publication Laid open No. 229400/1984 (laid open in Japan on Dec. 22, 1984) is mentioned an IC card wherein IC chips are fitted to a base and an electroconductive layer is provided at least around the IC chips. Particularly in FIGS. 2 and 4 to 7 thereof is mentioned "external terminal 6" thought to correspond to the external contact terminal at issue in the present invention. However, the necessity for structural feature and formation of this "external terminal 6" are not in this data.
As in the above, in the Unexamined Japanese Patent Publication laid open No. 26451/1981 and 229400/1984, the necessity for structural feature and formation of each of the "contact surface 20" and "external terminal 6" thought to correspond to the external contact terminal at issue in the present invention are not disclosed because it was very difficult with the technique in those days to form it so as to satisfy the above described limitation relating to thickness and the like. Particularly, using the general technique in those days that such external contact terminal is formed simultaneously with the other conductor circuit 13 on the surface of the IC module 12, it was very difficult to form the external contact terminal having a predetermined thickness. Therefore, the formation of the external contact terminal of the type at issue in the present invention could not be disclosed at all in the above mentioned Patent Gazette.
The formation of the external contact terminal using this conventional technique as considered on the basis of the conventional technical level known to the inventors is as follows. The conductor circuit 13 and external contact terminal are formed on the surface of the IC module 12 usually by etching the conductor foil on the IC module 12. As shown in FIG. 21, an etching mask 14 is applied to the conductor foil surface on the surface of the IC module and the range shown by the two-point chain lines is left through this etching mask 14. However, it is very difficult to etch this conductor foil on the lines at right angles with the etching mask 14. As shown in FIG. 22, the side of the conductor circuit 13 or external contact terminal formed by etching is not etched at right angles but is curved by the impregnation with the etching liquid. With such shape, the side of the conductor circuit 13 or external contact terminal will be deformed. If the external contact terminal is to be laminated with the over sheet 32 so as to expose the surface, the end part of the over sheet 32 will ride on a part of the side of the external contact terminal and, as shown in FIG. 22, the external contact terminal will not be able to be actually laminated with the over sheet 32 so as to be flush with the surface of the external contact terminal.
This shall be described in more detail. In the case of etching a metal such as a copper foil, the etching factor will be about 2. Therefore, the side of the external contact terminal will not be at right angles but can be a slope at an angle of up to 60 degrees. Further, in the case of a metal 0.1 to 0.3 mm thick, the width of the part of this slope will reach 0.05 to 0.15 mm. Therefore, as shown in FIG. 22, in the case of laminating the IC module 12 with the over sheet 32, a gap will be made between the sides of the external contact terminal, the over sheet 32 will overlap on the above mentioned slope and the surface of the over sheet 32 will not be flush with the surface of the external contact terminal. Thus, the lamination with the over sheet 32 will be impossible. over sheet 32 will be impossible.